1. Field of Endeavor
The present invention relates to communication systems, and more particularly to a system for acoustic communication in a fluid-filled pipe or a network of fluid-filled pipes.
2. State of Technology
In U.S. Pat. No. 6,082,193 issued Jul. 4, 2000, Paulson uses an array of acoustic (passively listening) sensors along a cable deployed in a fluid-filled pipe to monitor the pipe status. The patent states “a cable is deployed in the pipeline, with at least one acoustic sensor attached. The acoustic sensor is selected to detect acoustic emissions in the fluid in which it is put. The acoustic emissions are those generated by an acoustic event in a pipeline such as emissions produced by a wire break or a high pressure leak. In a preferred embodiment, the sensor is a hydrophone.” The use of these ‘cabled’ sensors is not practical in many pipe and pipeline systems due to the plurality of pipes.
Acoustic sensors have been proposed for water supply system monitoring. Savic, U.S. Pat. No. 5,416,724, uses passive (listening) acoustic transducers to monitor the sound generated within a pipe or pipe network filled with flowing fluid and distinguishes between acoustic signals originating from leaks and signals from ambient acoustic noise. His related patent U.S. Pat. No. 5,623,421 selectively identifies specific spectral lines from generally expected spectra. Sound generated by a leak is introduced into a digital processing and pattern recognition device to detect the presence of leaks.
United States Patent Application No. 2002/0189362 by Vladimir Havlena for communication for water distribution networks, published Dec. 19, 2002, provides the following state of technology information, “Control of processes is a broad general concern for every industry, particularly where fluids such as water are distributed in a network of pipes, vessels, containers and tanks. . . . One particular industry that requires significant control and which presently does not have adequate abilities for this goal is the water distribution networks that bring potable water from water supply sources and water treatment plants providing these water supply sources.” The patent describes a system whereby a remote sensor makes a measurement (in their case pressure or flow rate) on the fluid contained in a pipe, which may or may not be part of a network of pipes, and then transmits acoustically the reading to a centralized control station. They refer to the frequency band 3-11 kHz, with the upper limitation due to the nature of sound dispersion and attenuation while propagating in a finite sized medium (i.e., in a pipe). This frequency limitation poses severe limitations on their potential data transmission rates. They make no mention of using any signal processing, matched filter, or other signal extraction techniques.
In U.S. Pat. No. 6,389,881, Yang, et al., describe the use of sophisticated signal processing techniques, such as pattern match filtering, to identify failure in fluid filled pipes. In their application, they use the signal processing to deconvolve the signal of interest, i.e., the sounds related to pipe failure, from the ambient ‘noise’ resulting from the fluid flow in the pipe. The technique uses an array of passive, ‘listening’ acoustic transducers to monitor the fluid for sounds relating to pipe failure. The frequency range associated with these events is very low, approximately 0.01 Hz to 10 Hz.
Accordingly, it would be of great advantage in the field if a system enabling high data transfer acoustic communication in fluid filled pipes could be implemented. Various applications of such a system could include wireless monitoring/control of remote operated submersible vehicles used for pipe inspection in hostile environments (e.g., power plant coolant drain pipes) and wireless communication in pipes or pipelines (e.g., from remote sensors monitoring the pipe itself or the fluid contained therein).